High plasma levels of human immunodeficiency virus type 1 (HIV-1) RNA are found during primary infection with HIV-1, the seroconversion illness, [C. Baumberger et al, AIDS, 7:(suppl 2):S59 (1993); M. S. Saag et al, Nature Med., 2:625 (1996)], after which they subside as the immune response controls the infection to a variable extent. Post seroconversion, lower but detectable levels of plasma HIV-1 RNA are present, and these levels rise with disease progression to again attain high levels at the AIDS stage [M. S. Saag et al, Nature Med., 2:265 (1996)]. Approximately 50% of subjects have a symptomatic illness at seroconversion [B. Tindall and D. A. Cooper, AIDS, 5:1 (1991)] and symptomatic seroconversion is associated with an increased risk for the development of AIDS, probably because a severe primary illness is likely related to an early and extensive spread of HIV.
Inhibition of viral multiplication during the initial infection will likely reduce the subsequent development of chronic viremia leading to AIDS. Current medical practice, with administration of antiviral drugs for defined "at risk" situations, such as needle sticks with contaminated blood or pregnancy in HIV infected mothers, supports this concept.
Post seroconversion levels of HIV-1 RNA in plasma have proven to be the most powerful prognosticator of the likelihood of progression to AIDS [J. W. Mellors et al, Science, 272:1167 (1996); M. S. Saag et al, Nature Med., 2:265 (1996); R. W. Coombs et al, J. Inf. Dis, 174:704 (1996); S. L. Welles et al, J. Inf. Dis., 174:696 (1990)]. Other measures of viral load, such as cellular RNA [K. Saksela et al, Proc. Natl. Acad. Sci. USA, 91:1104 (1994)] and cellular HIV proviral DNA [T-H. Lee et al, J. Acq. Imm. Def. Syndromes, 7:381 (1994)] similarly establish the importance of the initial infection in establishing viral loads that determine future disease progression.
Thus, any intervention that inhibits HIV-1 infectivity during initial infection and/or lowers viral load post sero-conversion is likely to have a favorable influence on the eventual outcome, delaying or preventing progression to AIDS.
A variety of methods are now employed to treat patients infected with human immunodeficiency virus (HIV-1), including treatment with certain combinations of protease inhibitor drugs. Unfortunately, however, this type of treatment is associated with serious side effects in some patients. Alternatively, vaccines are under development for control of the spread of HIV-1 to uninfected humans. However, this effort has largely been directed to proteins of the virus, expressed on the surface of infected cells, which are recognized by cytotoxic T cells with elimination of the infected cells, while free virus is blocked and cleared by antibody to surface antigens of the virion. Limitations of this mode of vaccination are readily apparent for HIV-1, which has demonstrated a great diversity in immunogenic viral epitopes and rapid mutational variations that occur within and between individuals [B. D. Preston et al., Science, 242:1168(1988); J. D. Roberts et al., Science, 242:1171 (1988); A. R. Meyerhans et al., Cell, 58:901 (1989); K. Kusumi et al., J. Virol, 66:875 (1992); B. A. Larder et al., Science, 243:1731 (1989); M. S. Sang et al., N. Engl. J. Med., 329:1065 (1993); M. A. Sande, et al., JAMA, 270:2583 (1993); M. Seligmann et al., Lancet, 343:871 (1994); G. Meyers et al., Human retroviruses and AIDS 1993, I-V. A compilation and analysis of nucleic acid and amino acid sequences. Los Alamos National Laboratory, Los Alamos, N. Mex.]
Variation in strains of HIV-1 and frequent mutations of virion proteins have prevented successful application of conventional vaccine approaches [W. E. Paul, Cell, 82:177 (1995); J. E. Osborn, J. Acq. Imm. Def. Syndr. Hum. Retrovirol., 9:26 (1995)]. Mutation and selection of resistant variants is the central problem in developing a successful HIV-1 vaccine [M. D. Daniel et al., Science, 258:1938 (1992); N. L. Letvin, N. Engl. J. Med., 329:1400 (1993); M. Clerici et al., AIDS, 8:1391 (1994); S. M. Wolinsky et al, Science, 272:537 (1996)].
Other approaches to HIV-1 treatment have focused on the transactivating (tat) gene of HIV-1, which produces a protein (Tat) essential for transcription of the virus. The tat gene and its protein have been sequenced and examined for involvement in proposed treatments of HIV [see, e.g., U.S. Pat. No. 5,158,877; U.S. Pat. No. 5,238,882; U.S. Pat. No. 5,110,802; International Patent Application No. WO92/07871, published May 14, 1992; International Patent Application No. WO91/10453, published Jul. 25, 1991; International Patent Application No. WO91/09958, published Jul. 11, 1991; International Patent Application No. WO87/02989, published May 21, 1987]. Tat protein is released extracellularly, making it available to be taken up by other infected cells to enhance transcription of HIV-1 in the cells and to be taken up by noninfected cells, altering host cell gene activations and rendering the cells susceptible to infection by the virus. Uptake of Tat by cells is very strong, and has been reported as mediated by a short basic sequence of the protein [S. Fawell et al., Proc. Natl. Acad. Sci., USA, 91:664-668 (1994)].
International Patent Application No. WO92/14755, published Sep. 3, 1992, relates to the Tat protein and to the integrin cell surface receptor capable of binding to the Tat protein. Two Tat sequences that bind integrin are identified, which are the basic region or domain which is the dominant binding site for the integrin, having a peptide sequence of -Arg-Lys-Lys-Arg-Arg-Gln-Arg-Arg-Arg- [SEQ ID NO: 4], as well as -Gly-Arg-Gly-Asp-Ser-Pro- [SEQ ID NO: 5]. This specification demonstrates that a number of peptides corresponding to these Tat sequences and the corresponding integrins block in vitro cell binding to Tat coated plates, as do antibodies to the appropriate integrins. However, the specification also shows that these reagents do not block uptake of functional Tat by cells (see Example 9 in WO92/14755), thus nullifying the proposed mechanism of action for therapeutic benefit in HIV infection. The Tat sequences described in this international application are distinct from the peptide immunogens of the present invention.
Both monoclonal and polyclonal antibodies to Tat protein have been readily produced in animals and shown to block uptake of Tat protein in vitro [see, e.g., D. Brake et al, J. Virol., 64:962 (1990); D. Mann et al, EMBO J., 10:1733 (1991); J. Abraham et al, cited above; P. Auron et al, cited above; M. Jaye et al, cited above; G. Zauli et al, cited above]. More recent reports showed that monoclonal or polyclonal antibodies to Tat protein added to tissue culture medium attenuated HIV-1 infection in vitro [L. Steinaa et al, Arch. Virol., 139:263 (1994); M. Re et al, J. Acq. Imm. Def. Syndr. Hum. Retrovirol., 10:408 (1995); and G. Zauli et al, J. Acq. Imm. Def. Syndr. Hum. Retrovirol., 10:306 (1995)].
The inventor's own publication [G. Goldstein, Nature Med., 2:960 (1996); see also, International Patent Application No. WO95/3 1999, published Nov. 30, 1995] reviewed the evidence indicating that secretion of HIV-1 Tat protein from infected cells and uptake by both infected and uninfected cells was important for the infectivity of HIV-1. Previous studies also showed that antibodies to Tat protein in vitro blocked uptake of Tat and inhibited in vitro infectivity. Goldstein proposed active immunization of mammals to induce antibodies to HIV-1 Tat protein as a potential AIDS vaccine.
Despite the growing knowledge about HIV-1 disease progression, there remains a need in the art for the development of compositions and methods for treatment of HIV-1, both prophylactically and therapeutically, which are useful to lower the viral levels of HIV-1 for the treatment and possible prevention of the subsequent, generally fatal, AIDS disease.